The present invention relates to the art of shift registers and more particularly, to serial access, thin magnetic film memories using domain walls for the storage and propagation of binary information. Prior thin-film shift register art discloses serial access memories with storage and propagation of reversal domains, e.g., U.S. Pat. No. 3,846,770, and inversion of Neel walls with storage and propagation of Block lines, crossties, and inverted Neel walls along a domain wall, e.g., U.S. Pat. No. 3,868,659.
In the crosstie memory, the combination of a Bloch line, negative Neel wall and a crosstie are considered to be a logical "one," while the absence of this Bloch line-crosstie pair is considered to be a logical "zero." With a single conductor placed above and parallel to serrated strips of permalloy about 370 A thick and twenty-five microns wide, it is possible to effect propagation. A small amplitude (e.g., about 3.0 Oerstads) negative pulse about twenty nanoseconds long is used to move the Bloch line to the next potential well. Then a ten nanosecond positive pulse of about fifteen Oerstads is applied to relocate the crosstie. During application of the large positive pulse a new crosstie Bloch line pair is formed within the original Bloch line crosstie pair and the trailng Bloch line crosstie pair is annihilated. Thus, the original Bloch line and a new crosstie end up one serration farther along the strip. This technique worked for pulses with amplitude and time duration tolerances of only a few percent. Attempts to increase the tolerances of operation have been unsuccessful. A more detailed description of the nucleation and propagation of Bloch line-crosstie pairs appears in U.S. Pat. No. 4,100,609.